Insulinoma laboratory tests

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Amandeep Singh M.D.[2]

Overview

Laboratory findings consistent with the diagnosis of insulinoma include serum glucose < 55 mg/dL, serum Insulin > 5-10 μU/mL, serum C-Peptide > 200 pmol/L, and serum proinsulin ≥ 22 pmol/L. Patients with insulinoma may have elevated insulin to glucose ratio of > 0.4, which is usually suggestive of insulinoma after a 72-hour fast test(gold standard test). 33% patients have clinical symptoms within 12 hours of the fasting, 80% develop within 24 hours, 90% develop within 48 hours, and 100% develop within 72 hours.

Laboratory Findings

• Laboratory findings consistent with the diagnosis of insulinoma include:
  • Serum glucose < 55 mg/dL
  • Serum Insulin > 5-10 μU/mL
  • Serum C-Peptide > 200 pmol/L
  • Serum proinsulin ≥ 22 pmol/L
• Patients with insulinoma may have elevated insulin to glucose ratio of > 0.4, which is usually suggestive of insulinoma after a 72-hour fast test. It is a gold standard test.
  • 33% patients develop clinical symptoms within 12 hours of the fasting
  • 80% develop clinical symptoms within 24 hours of the fasting
  • 90% develop clinical symptoms within 48 hours of the fasting
  • 100% develop clinical symptoms within 72 hours of the fasting